In the current year we have isolated the plaque particle from the sheep urinary bladder using rather mild experimental conditions (exposure of the isolated lumenal plasma membrane to trypsin at 0.05 mg per mg protein at room temperature for fifteen minutes). Our immediate goal is to purify this protein, to analyze its subunit composition, to determine its lipid associations and to describe its specific insertion within the membrane structure. Since this large particulate structure serves as a morphological marker for the normal urothelial surface membrane but appears to be absent in surface membranes from abnormal bladders, we propose to analyze surface membranes of hyperplastic and neoplastic urothelia in rats with respect to surface membrane components in general and to the plaque proteins in particular using the immunocytochemical technique already established in our laboratory. To establish the progression of change in surface membrane components, we propose to have rats poised in the different stages depicting the advancement of chemically (FANFT) induced carcinogenesis. These studies should enable us to describe some of the fundamental events occurring at the very early stages of carcinogenesis and could possibly find clinical significance.